The present invention relates to an arc welding apparatus. More particularly, the invention relates to a circuit arrangement for facilitating the setting of welding conditions for a TIG (tungsten-inert gas) welding apparatus in which a filler wire is heated to a high temperature by resistance heating caused by a current flowing through the filler wire, and is fed to the weld.
FIG. 1 is a circuit block diagram showing a conventional welding apparatus of the type described. The welding apparatus includes a welding power supply 1 having output terminals to which there are connected a tungsten electrode 2 and a workpiece 3, respectively, for producing an arc 4 therebetween to melt a portion of the workpiece 3. The welding apparatus also includes a wire heating power supply 5 having output terminals, one coupled to the workpiece 3 with the other to a current feeder tip 7 for supplying an electric current to a filler wire 6. The wire heating power supply 5 supplies the current which flows through the workpiece 3, the filler wire 6, the current feeder tip 7 and back to the wire heating power supply 5, whereupon the filler wire 6 is heated to a high temperature due to resistance heating as it automatically fed into the weld puddle at the welding junction by a filler wire feeder (not shown).
A control unit for the welding apparatus of FIG. 1 is illustrated in block form in FIG. 2. Identical parts are denoted by identical reference numerals in FIGS. 1 and 2. The current flowing from the electrode 2 to the workpiece 3 is kept constant by comparing, in a comparator 9, an output from a current detector 11 with a command from an output current setting unit 8, and controlling an output regulator 10 to produce a constant current. The current which flows through the filler wire 6 is controlled by comparing, in a comparator 13, an output from a wire voltage setting unit 12 with an output from a wire voltage detector 15, and commanding an output regulator 14 for applying a constant voltage to the filler wire 6. The circuit of FIG. 2 is described in more detail in co-pending U.S. patent application Ser. No. 39,766. Some conventional apparatus put to use prior to the illustrated arrangement have no voltage feedback loop for the wire voltage as shown in FIG. 2. The filler wire 6 is fed to the weld puddle by wire drive rollers 19 driven by a motor 18 energized by a motor driver circuit 17 under the control of wire feed setting unit 16. FIG. 3 is a circuit diagram showing the filler wire feeding section having the motor driver circuit 17, the motor 8 and the rollers 19 in detail. The circuit 17 is of a well known thyristor Leonard system in which the firing angle of the thyristor is controlled by the output of the unit 16.
With the prior welding apparatus as described above, the current for melting the workpiece, the amount of feed of the filler wire for providing a desired amount of filler deposition, and the wire voltage for enabling the filler wire to be melted into the weld puddle under good conditions have independently been adjusted. It has been quite tedious and time-consuming to effect independent adjustment of these three conditions for optimum welding conditions, and it has required accumulated experience and much skill on the part of the operator.